| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 36°F | 29°F | 4.0" |
| February | 23°F | 36°F | 29°F | 3.7" |
| March | 33°F | 50°F | 40°F | 5.2" |
| April | 44°F | 63°F | 52°F | 4.8" |
| May | 54°F | 70°F | 61°F | 5.1" |
| June | 61°F | 77°F | 68°F | 5.8" |
| July | 66°F | 81°F | 73°F | 4.0" |
| August | 64°F | 79°F | 71°F | 4.3" |
| September | 56°F | 70°F | 62°F | 4.4" |
| October | 48°F | 62°F | 55°F | 5.6" |
| November | 37°F | 51°F | 43°F | 3.8" |
| December | 29°F | 41°F | 35°F | 5.0" |
| Index | Frederick | Maryland | National |
| Air quality index | 40 | 43 | 42 |
| Pollution index | 5,553,870 | 5,342,367 | 2,726,193 |
| Measurement | Total |
| Days measured | 362 |
| Days with good air quality | 306 |
| Days with moderate air quality | 54 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.004% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.410% |
| Mercury | 0.070% |
| City | Population | Air Quality Index | National Avg. |
| Ballenger Creek, MD | 21,484 | 40 | 20.0% |
| Buckeystown, MD | 1,289 | 40 | 20.0% |
| Monrovia, MD | 1,556 | 40 | 20.0% |
| Rosemont, MD | 325 | 40 | 20.0% |
| Brownsville, MD | 26 | 40 | 20.0% |
| Frederick, MD | 71,843 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Decatur, IL | 71,857 | 44 | 12.0% |
| Lauderhill, FL | 71,827 | 41 | 18.0% |
| Pawtucket, RI | 71,821 | 44 | 12.0% |
| Pittsburg, CA | 71,723 | 40 | 20.0% |
| Redlands, CA | 71,680 | 89 | 78.0% |
| Frederick, MD | 71,843 | 40 | 20.0% |
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